BACKGROUND. Through a shRNA synthetic lethal screen we have identified a number of mRNA splicing factors that are required for the viability of KRAS mutant cancer cells. PURPOSE. In this project we aim to address the following questions: 1) the mechanism by which depletion of mRNA splicing factors causes synthetic lethality with the KRAS oncogene; 2) which cellular mRNAs are differentially spliced in KRAS mutant cells; 3) how the changes in mRNA splicing pattern in KRAS mutant cells affect their viability compared to KRAS wild type cells. SIGNIFICANT MATERIALS AND METHODS. 1) shRNAs that target splicing factors. 2) RNA-seq protocol for quantifying mRNA splicing pattern changes. FY2013 ACCOMPLISHMENT. In 2012 we have carried out RNA-seq experiments to characterize mRNA splicing patters in KRAS wild type and mutant cells with or without splicing factor knockdown. We have identified candidate genes whose splicing and expression are critical for the viability of KRAS mutant cells and we demonstrated that expression of cDNAs of these candidate genes, which do not require the mRNA splicing machinery, could partially rescue the loss of mRNA splicing factors in KRAS mutant cells. We are currently preparing a manuscript for publication.